2.6 + 2.7

What happens in meiosis?

• diploid genetic material is reduced to haploid amount

Sporophyte stage

• diploid

• life cycle alternation for multicellular plants

Gametophyte stage

• haploid

• life cycle alternation for multicellular plants

Why are chromosomes invisible during interphase?

Because DNA exists as dispersed chromatin fibers in the nucleus

What happens to chromatin fibers when mitosis begins?

They coil and fold, condensing into visible mitotic chromosomes.

What is revealed when mitotic chromosomes are loosened?

Individual fibers similar to those seen in interphase chromatin

Why are few fiber ends observed in mitotic chromosomes?

Because the fibers loop back into the interior of the chromosome.

How are chromatin fibers arranged within mitotic chromosomes

They are twisted and coiled around one another in a regular folding pattern.

What occurs to chromosomes during late telophase and G1?

They unwind and return to long chromatin fibers.

What is chromatin composed of?

DNA and associated proteins, particularly histones.

Why is the chromatin arrangement important during interphase?

It allows DNA to function efficiently in transcription and replication.

What is the structure of a metaphase chromosome?

It consists of two sister chromatids joined at a centromere.

How does each chromatid arm appear structurally?

As a single continuous fiber coiled like a skein of yarn.

What is the folded-fiber model?

A model proposed by Ernest DuPraw describing how chromatin fibers fold to form mitotic chromosomes.

What is the composition of the chromatid fiber?

Tightly coiled double-stranded DNA and protein.

How much DNA compaction occurs from interphase to prophase?

Approximately a 5000-fold reduction in length.

Why must chromosome condensation be precise?

To maintain the highly ordered and consistent structure of chromosomes in all eukaryotes.

How are sister chromatids connected before anaphase?

They are joined only at their shared centromere.